The present invention is directed to an imaging method and apparatus and, in particular, it is directed to an imaging method and apparatus wherein electrostatic latent images are formed on imaging members where they are rendered visible with toner particles, followed by transfer of the toner images to an intermediate transfer member followed by transfer with very high efficiency to a permanent substrate.
Imaging processes wherein a developed image is first transferred to an intermediate transfer means and subsequently transferred from the intermediate transfer means to a substrate are known. For example, U.S. Pat. No. 3,862,848 (Marley), discloses an electrostatic method for the reproduction of printed matter in which an electrostatic latent image is developed by the attraction of electroscopic marking particles thereto and is then transferred to a first receptor surface by the simultaneous application of contact and a directional electrostatic field of a polarity to urge the marking particles to the receptor surface, with the image then being transferred from the first receptor surface to a second receptor surface by the simultaneous application of contact and a directional electrostatic field of opposite polarity to urge the marking particles to the second receptor surface.
In addition, U.S. Pat. No. 3,957,367 (Goel), discloses a color electrostatographic printing machine in which successive single color powder images are transferred, in superimposed registration with one another, to an intermediary. The multi-layered powder image is fused on the intermediary and transferred therefrom to a sheet of support material, forming a copy of the original document.
Further, U.S. Pat. No. 4,341,455 (Fedder), discloses an apparatus for transferring magnetic and conducting toner from a dielectric surface to plain paper by interposing a dielectric belt mechanism between the dielectric surface of an imaging drum and a plain paper substrate such that the toner is first transferred to the dielectric belt and subsequently transferred to a plain paper in a fusing station. The dielectric belt is preferably a material such as Teflon or polyethylene to which toner particles will not stick as they are fused in the heat-fuser station.
U.S. Pat. No. 3,893,761 (Buchan et al.), discloses an apparatus for transferring non-fused xerographic toner images from a first support material, such as a photoconductive insulating surface, to a second support material, such as paper, and fusing the toner images to the second support material. Such apparatus includes an intermediate transfer member having a smooth surface of low surface free energy below 40 dynes per centimeter and a hardness of from 3 to 70 durometer. The intermediate transfer member can be, for example, a 0.1 to 10 mil layer of silicone rubber or a fluoroelastomer coated onto a polyimide support. The member can be formed into belt or drum configuration. Toner images are transferred from the first support material to the intermediate transfer member by any conventional method, preferably pressure transfer. The toner image is then heated on the intermediate transfer member to at least its melting point temperature, with heating preferably being selective. After the toner is heated, the second support material is brought into pressure contact with the hot toner whereby the toner is transferred and fused to the second support material.
U.S. Pat. No. 4,682,880 (Fujii et al.), discloses a process wherein an electrostatic latent image is formed on a rotatable latent image bearing member and is developed with a developer into a visualized image. The visualized image is transferred by pressure to a rotatable visualized image bearing member. The steps are repeated with different color developers to form on the same visualized image bearing member a multi-color image which corresponds to one final image to be recorded. The latent image bearing member and the visualized image bearing member form a nip therebetween through which a recording material is passed so that the multi-color image is transferred all at once to a recording material.
"Color Xerography With Intermediate Transfer," J. R. Davidson, Xerox Disclosure Journal, volume 1, number 7, page 29 (Jul. 1976), the disclosure of which is incorporated herein by reference, discloses a xerographic development apparatus for producing color images. Registration of the component colors is improved by the use of a dimensionally stable intermediate transfer member. Component colors such as cyan, yellow, magenta, and black are synchronously developed onto xerographic drums and transferred in registration onto the dimensionally stable intermediate transfer member. The composite color image is then transferred to a receiving surface such as paper. The intermediate transfer member is held in registration at the transfer station for transferring images from the xerographic drums to the member by a hole-and-sprocket arrangement, wherein sprockets on the edges of the drums engage holes in the edge of the intermediate transfer member.
U.S. patent application Ser. No. 07/513,406 filed on Apr. 23, 1990 in the name of Berkes et al and assigned to the same assignee as the instant application discloses an imaging apparatus and process wherein an electrostatic latent image is formed on an imaging member and developed with a toner, followed by transfer of the developed image to an intermediate transfer element and subsequent transfer with very high transfer efficiency of the developed image from the intermediate transfer element to a permanent substrate, wherein the intermediate transfer element has a charge relaxation time of no more than about 2.times.10.sup.2 seconds.
Intermediate transfer elements employed in imaging apparatuses in which a developed image is first transferred from the imaging member to the intermediate and then transferred from the intermediate to a substrate should exhibit both good transfer of toner material from the imaging member to the intermediate and very good transfer of toner material from the intermediate to the substrate. Very good transfer occurs when most or all of the toner material comprising the image is transferred and little residual toner remains on the surface from which the image was transferred. Very good transfer is particularly important when the imaging process entails generating full color images by sequentially generating and developing images in each primary color in succession and superimposing the primary color images onto each other on the intermediate, since undersirable shifting or color deterioration in the final colors obtained can occur when the primary color images are not efficiently transferred from the intermediate to the substrate (paper).
Although known methods and materials are suitable for their intended purposes, a need remains for imaging apparatuses and methods employing intermediate transfer elements with high transfer efficiency to a final substrate. In addition, there is a need for imaging apparatuses and methods employing intermediate transfer elements that enable generation of full color images with high color fidelity.